The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Multicast technology is a one-to-many multiparty communication technology. Being different from a commonly used unicast technology, the multicast technology reduces the replication of data content by setting up an optimized multicast forwarding path, thereby greatly reducing the network resources occupied in the multiparty communication.
Currently, multiple protocol label switch (MPLS) technology is a routing technology widely applied to the IP network, in which a label distribution protocol (LDP), a protocol for distributing labels among routers adopting the MPLS protocol, is often adopted in terms of label distribution. In the past, the MPLS is usually adapted to forward unicast IP packets. With the development of the multicast technology, it gradually becomes a researching focus to realize multicast through the MPLS technology. Recently, it has become an important development direction for the existing MPLS multicast to set up a point-to-multipoint (P2MP) label switching path (LSP) tunnel and a multipoint-to-multipoint (MP2MP) LSP tunnel through the LDP technology.
In the related art, the forwarding paths P2MP LSP and MP2MP LSP are set up through the LDP technology.
The P2MP LSP is set up according to a unicast routing protocol, and usually follows an optimized path principle. When the route is changed due to a certain reason, the LDP needs to determine a new optimized multicast LSP according to a route changing protocol, then sends a mapping request to a new upstream node, and sends a withdraw message to the former upstream node (which was the optimized one in the past but not the optimized one now). After such an adjustment, the multicast LSP becomes the optimized multicast LSP again. The method for adjusting the upstream node when the P2MP LSP forwarding path is set up is the same as that for adjusting the upstream node when the MP2MP forwarding path is set up. The P2MP is taken as an example herein, and the processing procedures thereof are shown in FIG. 1.
At first, in the P2MP LSP, a packet is forwarded from node R1 to R4 through R2, from R4 to R5 and R6, and from R6 to R7.
When the above route is changed due to a certain reason, by means of calculating according to the LDP protocol, the node R4 finds out that the upstream node R2 thereof is no longer in the optimized route, and the node R3 becomes the upstream node in the optimized route. At this time, the node R4 sends a mapping message to the node R3, and sends a withdraw message to the node R2.
Then, intermediate procedures for reconstructing the LSP are described. After receiving the mapping message, the node R3 continues to send the mapping request to the former upstream node R1 thereof. After receiving the withdraw request, the node R2 withdraws the label binding with the node R4, and at the same time, continues to send the withdraw request to the upstream node R1 since it does not have any downstream node.
It can be known from the related art that, in the path adjustment procedures, it is possible that the former multicast LSP has already been withdrawn before the setting up of the new multicast LSP is finished. The data stream forwarding may be temporarily interrupted, and it may not be resumed until the setting up of the new multicast LSP is finished. Moreover, the common multicast communication does not have a retransmission mechanism, so the resulted losing of packets may seriously influence the quality of the multicast service.